Television is used to deliver entertainment and education to viewers. The source material (audio, video, etc.) is multiplexed into a combined signal which is then used to modulate a carrier. This carrier is commonly known as a channel. In terrestrial broadcasts, these channels correspond to government assigned frequencies and are distributed over the air. The program is delivered to a receiver that has a tuner that selects the signal from the air and delivers it to a demodulator, which in turn provides video to a display and audio to speakers.
Much of television content is valuable to its producers, therefore copyright holders want to control access, disallow re-transmission of content over the Internet, and restrict copies. Examples of such protected material include, but are not limited to, feature films and sporting events. Currently, television terrestrial broadcast systems do not generally use any sort of control measures such as encryption systems to prevent unauthorized copying of content.